The watercraft designs differ the size, shape, and propulsion of the watercrafts. For instance, contemporary watercraft designs implement sails, jet engines, fans, water-jet propulsion drives, paddle drives, and motor-driven propellers for propulsion. Each type of propulsion has unique advantages and disadvantages.
People use watercrafts for a variety of recreational and commercial activities, from pulling water skiers to transporting oil to racing. The large variety of uses for watercrafts have inspired specialized and general purpose designs of various sizes, shapes, and means of propulsion; including propeller driven motorized versions; which are generally available as an inboard, outboard or inboard-outboard. Watercrafts with inboard drives (“inboards”) typically have a motor mounted in the watercraft and a fixed-position propeller. Inboards are inherently simpler designs than watercrafts with outboard motor drives (“outboards”) or watercrafts with inboard-outboard drives (“IOs”), or stern drives, so they are usually lower cost and lower maintenance. Inboards typically include a rudder in the prop wash of the propeller to steer the watercraft. Placing the rudder in the prop wash improves the steering by increasing the amount of water being redirected by the rudder. In reverse, the rudder is not in the prop wash and, as a result, the inboards are difficult to maneuver in reverse, which is especially troublesome when attempting to maneuver the watercraft to a dock, onto a trailer or when preparing to pull a water skier.
Large watercrafts such as boats that are greater than 30 meters in length are typically inboards due to the cost and maintenance advantages of inboards. Unlike smaller boats such as boats that are about 3 to 8 meters in length, the added cost and weight to mount side thrusters is less significant for large boats.
Outboards have one or more outboard motors mounted at the stern of the boat. A motor is located at the top of the outboard drive and is connected to a propeller at the bottom of the drive via a transmission and a substantially vertical shaft.
In many outboard designs, the outboard drive may rotate approximately 110 degrees in the horizontal plane, depending upon the design, to provide steering and can be tilted vertically to raise the propeller above the bottom of the hull to protect the propeller when the watercraft is in shallow water or transported or stored out of water. Because outboard drives typically have only one reverse, and one forward gear, the gear may provide too much thrust even in idle to easily dock the boat, which forces the person docking the boat to repeatedly switch between in gear and neutral to achieve slower speeds than possible at idle. Also, when maneuvering to remove slack in a ski rope, idle speed is typically too fast.
IOs have stern drives, which locate the motor inside the boat at the stern. The motor is connected through the transom to an outboard drive unit similar to the bottom half of an outboard motor. IOs provide steering by allowing the outboard drive unit to pivot about a substantially vertical axis. IOs are far more popular than standard inboards partly because they are easier to steer, especially in reverse. Yet, idle speed in both forward and reverse is typically too fast for docking and for removing slack in a ski rope.